pwritev() doesn't work anymore on i386

[Gianluca Borello]

I just upgraded to Trusty, and the following programs fails on x86:

#include <stdio.h>
#include <stdint.h>
#include <sys/uio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main()
{
 char *str0 = "hello ";
 char *str1 = "world\n";
 struct iovec iov[2];
 ssize_t nwritten;
 int fd = open("test.txt", O_CREAT | O_WRONLY);

 iov[0].iov_base = str0;
 iov[0].iov_len = strlen(str0);
 iov[1].iov_base = str1;
 iov[1].iov_len = strlen(str1);

 nwritten = pwritev(fd, iov, 2, 0);
 if(nwritten < 0)
  perror("pwritev");

 return 0;
}

Compiled without any flags, I see:

$ ./test
pwritev: File too large

And, from strace, I can see the offset parameter is handled wrongly by (presumably) libc:

...
pwritev(3, [{"hello ", 6}, {"world\n", 6}], 2, 577730142772658176) = -1 EFBIG (File too large)
...

If I compile with -D_FILE_OFFSET_BITS=64, everything is right, but is not a solution for my problem as I can't use that flag in my program.

I reported this here because it doesn't seem to happen on Debian sid, but let me know if I have to report it upstream.

$ lsb_release -rd
Description: Ubuntu 14.04 LTS
Release: 14.04

$ apt-cache policy libc6
libc6:
  Installed: 2.19-0ubuntu6
  Candidate: 2.19-0ubuntu6

[Gianluca Borello (g.borello)]

Any update on this?

[Michael Ferguson (mpfergu)]

I'm also encountering this bug with updated Ubuntu 14.04 but only on 32-bit installations.

I have another program to reproduce it, included below. This program
makes it to printing out OK on the 64-bit version.

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/uio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>

int main() {
  struct iovec vec[1];
  char* buf;
  size_t buflen = 4096;
  char* data = "aaaaaaaaaaaaaaaaaaaa";
  int datalen = strlen(data);
  int fd;
  ssize_t got;

  buf = malloc(buflen);
  assert(buf);
  vec[0].iov_base = buf;
  vec[0].iov_len = buflen;

  // open file
  fd = open("tmp.data", O_RDWR | O_CREAT, S_IRWXU);
  assert(fd>=0);

  // copy data to buf
  memset(buf, 0, buflen);
  memcpy(buf, data, datalen);
  vec[0].iov_base = buf;
  vec[0].iov_len = datalen;
  // write data
  got = pwritev(fd, vec, 1, 0);
  //got = pwrite(fd, buf, datalen, 0);
  if( got == - 1 ) perror("in write");
  assert(got == datalen);

  // clear buf
  memset(buf, 0, buflen);
  // read data
  vec[0].iov_base = buf;
  vec[0].iov_len = buflen;
  got = preadv(fd, vec, 1, 0);
  //got = pread(fd, buf, buflen, 0);
  if( got == - 1 ) perror("in read");
  assert(got == datalen);
  // check data
  assert(0 == memcmp(data, buf, datalen));

  close(fd);
  unlink("tmp.data");

  printf("OK\n");

  return 0;
}

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.